The present invention relates to a CDMA (Code Division Multiple Access) transmitter/receiver constructed to control the rise of transmission power of another station for thereby obviating a sharp increase in up-going interference wave level.
In a cellular communication system using a CDMA scheme, all mobile stations called by a base station effect CDMA multipath communication by sharing the same frequency. This deteriorates receipt reception quality due to, e.g., fading, and raises the interference wave level due to distance, thereby lowering the subscriber capacity of the system. To solve this problem, high speed, closed loop, transmission power control is essential.
Transmission power control executed by a conventional CDMA transmitter/receiver will be briefly described hereinafter on the assumption that a base station controls the up-going transmission power of a mobile station on the basis of reception quality from the mobile station. So long as a base station constantly receives up-going radio frames from a mobile station, the former can stably control the transmission power of the latter. However, when a building, for example, shades the mobile station, it is likely that the signal level on the effective path, which the base station has grasped, is lowered and sharply lowers reception quality although the up-going path may remain in synchronism. In such a case, the base station sends to the mobile station a transmission power control command for causing the mobile station to raise up-going transmission power. In response, the mobile station sharply raises its up-going transmission power.
Assume that the transmission power of a certain mobile station sharply increases when the base station is communicating with a plurality of mobile stations at the same time. Then, the sharp rise of the transmission power influences signals being received by the other mobile stations in the same manner as an increase in an interference wave. This prevents the number of mobile stations connectable to the base station at the same time from satisfying a capacity that depends on the system and thereby causes the CDMA communication system to fail. A scheme capable of preventing the up-going power from sharply increasing as a result of the temporary deterioration of up-going reception quality has not been reported in the past.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 5-22213, 9-284205, 10-108249 and 11-340948 as well as in Japanese Patent No. 2, 982, 856.